Kepler Mission Alex Kang Exoplanet History Scientific Goals Until the 1990s Astronomers had no method of detecting planets outside our solar system. The discovery of hot-Jupiter planets using radial velocity measurements spurred on the search. The radial velocity method discovered hundreds of planets until NASA’s 10th discovery mission came online. Kepler has been responsible for thousands of confirmed exoplanet discoveries. An idealized Light curve example Scientific Goals Defined by NASA, the specific scientific goals of the Kepler mission are as followed: Determine the percentage of terrestrial and larger planets that are in or near the habitable zone of a wide variety of stars Determine the distribution of sizes and shapes of the orbits of these planets Estimate how many planets there are in multiple-star systems Determine the variety of orbit sizes and planet reflectivities, sizes, masses and densities of short-period giant planets Identify additional members of each discovered planetary system using other techniques Determine the properties of those stars that harbor planetary systems. Artist rendition of Kepler Spacecraft Transit Method When a planet passes in front of a star, it blocks a portion of the light the star emits. This brightness decrease will occur periodically in sync with the period of the planets orbit. Measuring the light coming from a star with an orbiting planet for a long period of time will yield periodic brightness dips. These dips that occur from the transits are what the Kepler mission was designed to detect. A transit can only occur when the planet’s orbit is “edge-on” as seen from Earth. This means that the plane of the orbit must be parallel with our line of sight. If the plane was perpendicular no detections can occur. Kepler viewed the luminosity (brightness) of hundreds of thousands of stars simultaneously for just over 3 years. This data was then sent back to Earth where it could be processed. A histogram showing the sizes of the Kepler discoveries Mission End Kepler had a reaction wheel failure on July 14, 2012. The spacecraft has four such wheels to allow for precise aim for the telescope. The mission was still viable as long as the remaining three wheels remained operational On May 11, 2013 a second reaction wheel failed, halting the collection of science data and jeopardizing the entire mission. The Kepler mission came to an end officially on August 15, 2013 when NASA announced that they had given up attempting to fix the two broken reaction wheels. The spacecraft was then repurposed for the K2 “Second Light” mission. This would conduct research at a lower exposure time for other purposes not excluding exoplanet searches. The K2 Mission has discovered: 270 Candidate Exoplanets 39 Confirmed Exoplanets Some Notable Discoveries Kepler-10b – First rocky planet discovered Kepler-186f – First Earth-sized planet in the habitable zone Kepler-421b – Transiting exoplanet with longest known year (704 days, Mars at 780) Kepler-444 – roughly 11.2 billion year old system with five planets ranging in size from Mercury to Venus Candidate Exoplanets: 4696 Confirmed Exoplanets: 1041 Confirmed Earthlike Exoplanets: 12 A histogram showing exoplanets by detection methods Sources: http://www.nasa.gov/mission_pages/kepler/overview/index.html http://kepler.nasa.gov/Mission/QuickGuide/ http://www.nasa.gov/kepler/discoveries http://www.nasa.gov/mission_pages/kepler/spacecraft/index.html